In season 3 of Game of Thrones, it was Locke who

cut off Jaime Lannister's hand.

Locke is one of the men under the command of Roose Bolton. How did he end up in the Night's Watch?

Also, in S04E05, Locke tries to

abduct Bran Stark when he comes to know of his identity

But since in the same episode

He is killed by Hodor through Bran

What was his plan exactly?